Since a geodesic lens may be used in the transmission or reception of electromagnetic energy, it is customary to identify portions of a geodesic lens in terms of their function in the transmission of the electromagnetic energy while understanding that their functions may be reversed.
Goodman U.S. Pat. No. 3,343,171 discloses a modified helmet-type geodesic lens in which input lips are formed as partial cylinders whose axes are coincident with the major longitudinal axis of the lens and are joined to the outermost edges of the parallel plate conductors, which form the output lips of the lens, with semi-torroidal sections. This construction permits scanning the input lips along arcs centered on the longitudinal axis of the lens and displaced outwardly from the outermost edges of the output lips. In the transmission mode, focusing of collimated energy from a point source on these arcs is effected along an equi-phase line of collimated energy. The collimated energy is directed through the parallel plate conductors forming the output lips and then to a line source feed illuminating a parabolic cylinder reflector which transforms the rotating line of collimated energy to form a fan-shaped beam of collimated energy having an aperture dimension equal to the effective diameter of the lens in the scanning plane times the vertical aperture of the parabolic cylinder reflector in the non-scan plane. The fan-shaped beam in the far field of the antenna system can be moved, with exact one-to-one correspondence, by the arcuate movement of the feed horn. If the two input ports and also their associated reflectors are disposed 90.degree. apart, movement of a feed horn along one feed arc will scan a fan beam from the first reflector which moves in a plane orthogonal to the scan plane of the second reflector. Thus, this system achieves, in one lens system, the full capability of two fan beam track-while-scan (TWS) operations which previously had required two separate lens systems such as disclosed in the Hollis U.S. Pat. No. 2,841,770.
The Hollis U.S. Pat. No. 3,018,450 discloses a rotor ring switch comprising a plurality of sectors each having an output terminating in a feed horn. Such a ring switch can be employed with the Goodman system (U.S. Pat. No. 3,343,171).
However, dead time between scans may present a serious problem.